1. Field of the Invention
The invention relates generally to a computer implemented process for analysis of electrocardiogram signals and, more particularly, but not by way of limitation, it relates to an improved type of spectral filter for use in analyzing the electrocardiogram signal.
2. Description of the Prior Art
An early work related to the present invention is a publication entitled "Digital Filtering With Applications to Electrocardiogram Processing" by C. S. Weaver et al., IEEE Transactions on Audio and Electrocoustics; Vol. AU-16, No. 3, September, 1968, pp. 350-391. This publication discusses digital filtering in general and its possible applications to such as electrocardiogram processing. The paper discusses the design of low-pass, bandpass, high-pass, and notched filters using Z-transform techniques. The various filters are analyzed in relation to their use with the ECG wave form. A subsequent article entitled "Digital Filtering of the ECG--A Comparison of Low-Pass Digital Filters on a Small Computer" by T. P. Taylor et al.--Medical and Biological Engineering, July, 1974, pp. 493-502 discusses low-pass linear digital filters and their frequency, phase and impulse responses when used for filtering electrocardiograms.
Bi-directional digital filtering of ECG signals is described in a paper entitled "Late Potentials in Man and Cardiac Arrhythmias" by M. B. Simson et al., which appeared in Cardiovascular Section, Department of Medicine, University of Pennsylvania, pp. 255-264, 1981. An outgrowth from these basic teachings regarding the bi-directional type of digital filter is the subject matter of U.S. Pat. No. 4,422,459 in the name of M. B. Simson.
Digital filtering of electrocardiograms has also been extensively studied by an Israeli group as evidenced by the publication entitled "Non-Invasive Recording of Late Ventricular Activity Using an Advanced Method in Patients with a Damaged Mass of Ventricular Tissue" by Shimon Abboud et al. which appeared in Journal of Electrocardiology, Vol. 16, No. 3, 1983, pp. 245-252. More recent studies relate to the Fourier transform filter as analyzed in a publication entitled "Evaluation of Fourier Transform Filter for High-Resolution ECG" by D. W. Christenson et al. which appeared in Journal of Electrocardiology, Vol. 22 Supp., pp. 33-40, 1990. The FFT filter was used in connection with high-resolution electrocardiography in order to analyze the high-frequency content of ECG data to accentuate the high-frequency components thereby to enhance a new group of indicator signals.
Finally, in a publication entitled "Use of High-Pass Filtering to Detect Late Potentials in the Signal-Averaged ECG" by P. Lander and E. J. Berbari which appeared in Journal of Electrocardiology, Vol. 22, Supp. pp. 7-12, 1990, the authors analyze the various types of digital filter to derive advantages and disadvantages relative to ECG analysis. Thus, each of infinite impulse response filter (IIR), spectral window filter, and finite impulse response filter (FIR) were applied to the signal-averaged ECG to develop and analyze responses that readily disclose advantages and disadvantages of each type of filter. This study concludes that multiple filters may well be the best approach in providing full and positive analysis of the ECG waveform.